Consider this fact, some light waves like radio are large enough that a lot of matter is essentially invisible to their propagation; the radio waves just pass right by without any interactions. This becomes a similar problem when we try and measure such small quantum phenomena like zero-point energy. The quantum energy could be so small that they're invisible to our detectors, but are in fact still there - the two scales simple cannot interact in a measurable way. So, there'd like still be some quantum energy, just less and less until our detectors could not interact with the incredibly small quanta for measurement.